The invention relates to the field of intravascular delivery systems, and more particularly to dilatation balloon catheters.
Angioplasty balloons must be able to expand to a relatively large diameter in order to dilate stenosed regions of the vasculature effectively. However, it is also desirable for the angioplasty balloons to exhibit a minimal profile when deflated to facilitate introduction into and travel within the vasculature. A small crossing profile also allows the balloon to be positioned across the lesion. Furthermore, the deflated balloon should be sufficiently flexible to allow the balloon to be advanced through the often tortuous coronary anatomy.
To obtain a minimized deflated profile, the prior art has adopted various strategies to cause the balloon to preferentially fold into a compact shape when deflated. Typically, these strategies involve preformed creases that cause the balloon material to fold into flaps that then may be wrapped to minimize profile. Nevertheless, these attempts remain an incomplete solution to the problems of minimizing balloon profile.
One significant problem flows from the techniques used to manufacture the balloons. Typically, a parison is blow molded into the expanded balloon shape that generally comprises a main cylindrical section having a working diameter with flanking shoulder regions that provide a transition from the expanded working diameter of the balloon to the nominal diameter of the catheter. To provide sufficient material for blow molding in the areas corresponding to the working length, the parison must be relatively thick-walled. Upon expansion during blow molding, the material in the main cylindrical section is efficiently used leaving it relatively thin walled. However, the resulting wall thickness in the shoulder areas varies depending upon the final diameter. Since the areas at the extremities of the balloon essentially do not expand, the balloon material remains relatively thick in these areas. This varying wall thickness in the shoulder areas leads to inefficient folding and does not allow for an optimum deflated profile.
Another difficulty related to balloon folding results when the preformed creases converge in the shoulder regions. Where more than one crease occurs in a given area, the flaps of balloon material tend to stack, leading to increased profile and decreased flexibility.
Accordingly, there remains a need to provide angioplasty balloon designs that allow deflation to a small diameter while remaining flexible. Specifically, there remains a need for designs that minimize the difficulties resulting from the varying amount of balloon material in the shoulder regions. There is a corresponding need for methods of conveniently manufacturing such designs. This invention satisfies these and other needs.
The invention is an inflatable member comprising a generally cylindrical working length having an inflated diameter and opposing ends with tapered shoulder portions, wherein the shoulder portions are configured to minimize the deflated profile of the inflatable member. In a preferred embodiment, the shoulder portions have an asymmetric conic configuration. The asymmetry distributes the inflatable member material of the shoulder portions over a larger area than possible with a symmetrical configuration that reduces the inflatable member profile and improves flexibility. Optionally, the asymmetrical shoulder portions may also have spiraling preformed creases to facilitate folding. In an alternate embodiment, each shoulder portion has at least one triangular shaped pattern of preformed creases to optimize folding in the shoulder portion. Optionally, the shoulder portions may also have an asymmetric configuration and may have more than three preformed creases.
The inflatable members of the invention may generally be made by blow molding a conventional thermoplastic parison. Preferably, the mold is configured to produce inflatable members having the asymmetrical shoulder portions. The mold may also have ridges formed in the shoulder portion to provide the preformed crease in the blown inflatable member. Generally, the parison is placed within the mold, the mold is heated, and inflation fluid is supplied to the interior of the parison at sufficient pressure to expand it and conform it to the mold.